Vibration control apparatuses using inertia of an object are proposed as an apparatus to suppress transmission of vibration in a building structure or various mechanical apparatuses. Such vibration control apparatuses include an apparatus employing a mechanism for converting a linear motion into a rotational motion of a fly wheel to use the moment of inertia of the rotating fly wheel for vibration control so that the apparatus can be downsized.
Patent Literature 1 and Patent Literature 2 disclose apparatuses configured to convert a linear motion into a rotational motion using a ball screw and a ball nut to rotate a fly wheel disposed in a case and to include a viscous body, such as a synthetic rubber, disposed between the fly wheel and the case (see paragraph 0060, FIG. 6).
In such vibration control apparatus, a slight translational motion is amplified with the combination of the ball screw and the ball nut to rotate the fly wheel at a high speed, and the moment of inertia of the fly wheel and the viscous resistance produced between the fly wheel and the case can be used for vibration control.
A damping device which uses the viscosity and friction of a viscous magnetic fluid (MR fluid) for damping is proposed. Patent Literature 3 discloses a vibration control apparatus that uses a viscous magnetic fluid. FIG. 13 is a cross-sectional view illustrating a schematic configuration of a conventional damping device. The damping device 210 includes a cylinder 212 filled with a viscous magnetic fluid 211, a piston rod 213 inserted into the cylinder 212 and supported in the cylinder 212 so as to axially reciprocate, a piston 214 fixed at a suitable location in the middle of the piston rod 213 to partition the inside of the cylinder 212, a bypass tube 215 provided in the lower part of the cylinder 212, and a magnetic field generating unit 216, such as an electromagnet, disposed along the axial direction of the bypass tube 215. Attachment units 212a and 213a are provided on an end of the cylinder 212 and an end of the piston rod 213, respectively. The attachment units are attached, for example, to different portions of a building structure.
When a building is vibrated by, for example, an earthquake, the piston 214 moves in the cylinder along the axial direction to force the viscous magnetic fluid 211 to flow in the bypass tube 215. Under the effect of the magnetic field generated by the magnetic field generating unit 216, magnetic particles in the viscous magnetic fluid 211 form a chain-like structure to provide resistance in the flow of the viscous magnetic fluid 211 to damp the vibration.
According to the damping device 210, by controlling the current supplied to the electromagnet, which is the magnetic field generating unit, the damping property of the viscous magnetic fluid 211 can be adjusted to change the damping property of the damping device 210.